Failure to connect Float Out plugs to Color In plugs with Cycles shader nodes

[abelmilanes]

Version: Gaffer 1.3.7.0-linux
Third-party tools: Cycles
Third-party modules:

Description

Failure to connect Float Out plug to Color/Vector In plug with Cycles shader node. This happens even if the connection is made to individual [r,g,b] [x,y,z] values.
Also seem to happen when using nodes, but not when defining a Cycles Shader Network as an IECoreScene.ShaderNetwork() attribute via an expression.

It is possible however to connect individual [r,g,b] [x,y,z] values from Color/Vector Out plugs to Float In plugs.

Steps to reproduce

See attached gaffer script:

connection_bug.zip

Debug log

Click to Expand

WARNING : IECoreCycles::ShaderNetworkAlgo : Couldn't find socket input "color.b" on shaderNode "shader:d2a26e30a5ace686386e0b2ec1c6f291:emission1"
WARNING : IECoreCycles::ShaderNetworkAlgo : Couldn't find socket input "color.g" on shaderNode "shader:d2a26e30a5ace686386e0b2ec1c6f291:emission1"
WARNING : IECoreCycles::ShaderNetworkAlgo : Couldn't find socket input "color.r" on shaderNode "shader:d2a26e30a5ace686386e0b2ec1c6f291:emission1"

[johnhaddon]

Thanks for the clear repro steps. Looks like this just isn't handled at all in the Cycles backend - we have checks for when the connection source is an [ r, g, b] or [ x, y, z ] component, but not for when the destination is. It also looks like we're a bit wasteful and make multiple conversion nodes when a component-level source is used for multiple connections. Shouldn't be too big of a job to fix.

[johnhaddon]

I think the way we'll want to fix this is to add a variant of IECoreScene::ShaderNetworkAlgo::convertOSLComponentConnections() that works for any shader type, and allows you to specify what shaders to use for the intermediate conversions. Then we can call that from the Cycles backend rather than have a bunch more custom logic.

[johnhaddon]

I think the way we'll want to fix this is to add a variant of IECoreScene::ShaderNetworkAlgo::convertOSLComponentConnections() that works for any shader type, and allows you to specify what shaders to use for the intermediate conversions.

At the same time as doing this, I think we want to move away from using the MaterialX shaders as the default converters for Arnold networks, and use Arnold shaders instead.

[abelmilanes]

Thank you. Just tested 1.5.0.0 and this works as expected now.

[johnhaddon]

Thanks for testing!